A soft, supple and flexible skin has a marked cosmetic appeal and is an attribute of normal functioning epidermis.
As human skin ages with advancing years, the epidermis can become folded or ridged or furrowed to form wrinkles which signal the loss of youthful appearance and herald the transition to old age. This transition can occur prematurely with young people, especially those who expose themselves to excessive doses of sunlight. Also, the outer layer of the epidermis, that is the stratum corneum, can become dry and flaky following exposure to cold weather, or excessive contact with detergents or solvents which result in loss of skin moisture with the result that the skin loses its soft, supple and flexible characteristics.
Emollients such as fats, phospholipids and sterols have in the past been used to soften wrinkled or dry skin, but it is apparent that these emollients are only partially effective as a remedy for skin in poor condition.
The use of 2-hydroxyalkanoic acids for enhancing the quality of human skin following topical application thereto has already been described.
Thus, EP-A 0 007 785 (Unilever) discloses skin treatment compositions incorporating .alpha.-hydroxycaproic acid or .alpha.-hydroxycaprylic acid or mixtures thereof, the compositions having a pH value of less than 7, usually from 2 to 4.
It is also proposed in U.S. Pat. No. 4,105,782 (Yu & Van Scott) to use amines or ammonium salts of .alpha.-hydroxyacids in the treatment of acne or dandruff and, in the Yu & Van Scott patents U.S. Pat. No. 4,105,783 and U.S. Pat. No. 4,197,316, to use such compounds in the treatment of dry skin. U.S. Pat. No. 4,234,599 (Yu & Van Scott) discloses the use of .alpha.-hydroxyacids, and their esters or amine salts in the treatment of keratoses. In U.S. Pat. No. 4,363,815 (Yu & Van Scott) it is proposed to use .alpha.-hydroxyacids or .beta.-hydroxyacids or keto acids or their derivatives, in a composition for treating skin conditions.
According to GB 1 471 679 (Avon), it is known to use alkali metal salts of C.sub.2 -C.sub.5 .alpha.-hydroxycarboxylic acids in moisturising compositions.
In DE 2 110 993 (Henkel), there are disclosed alkali metal salts of C.sub.4 -C.sub.10 .alpha.-hydroxycarboxylic acids, and the sodium salt of .alpha.-hydroxycaprylic acid is mentioned.
In addition to premature ageing of human skin, as seen from the formation of wrinkles, other more immediate damaging effects of sunlight on skin have been observed since time immemorial, such as sunburn (erythema), keratoses and increased incidence of skin cancer (carcinoma), and many remedies have been proposed to protect the skin from this type of damage.
In general terms, harmful ultra-violet radiation, particularly that originating from sunlight, which penetrates the upper atmosphere and reaches the earth's surface, can be classified into:
i. the energy-rich UV-B rays (290-320 nm wavelength) which possess an intense physiopathological activity on the skin; these are absorbed just above the dermis and they are responsible for erythema and skin pigmentation, and
ii. UV-A rays (320-400 nm wavelength) which penetrate deeper into the skin (to the dermis and beyond). Their energy is much lower and the photobiological effects they cause are much more long term in nature, for example, they accelerate skin ageing. Certain organic substances (sunscreens) whose molecules absorb the harmful ultra-violet rays have been proposed for use; these substances mitigate the deleterious effects of ultra-violet radiation.
Some of these substances absorb more effectively in UV-A range thereby providing filtering of UV radiation in this range, while others are more effective in the UV-B range.
A common problem exists, however, whatever the choice of organic sunscreen, for protection from whichever wavelength of ultra-violet radiation, and this is that physiological damage to the body can occur, following topical application of these sunscreens in quantities necessary to provide effective filtering of harmful ultra-violet radiation. Even those organic sunscreens that are believed to be safe to use in this way, necessarily have safety limits imposed, based on the quantity applied to the skin, which can result in only moderate to poor protection from harmful ultra-violet radiation.
Certain inorganic substances which physically block ultra-violet exposure of the skin have also been proposed for use as sunscreens. Notable of these is titanium dioxide having a very small particle size. This grade of titanium dioxide, designated ultrafine (also described as micronised) TiO.sub.2, affords a good degree of sun blocking potential without the unacceptable skin whitening experienced with the normal pigmentary grade (particle size &gt;300 nm). For example, in DE-A-3824999 (The Boots Company PLC), it is proposed to use titanium dioxide with a mean primary particle size of &lt;100 nm in a water-in-oil emulsion as a sunscreen preparation. This reference also suggests that additional organic sunscreen agents, such as p-aminobenzoic acid and esters thereof, methoxycinnamate, benzophenone, dibenzoylmethanes or salicylates can also be included to improve protection.
In spite of this and other prior proposals, there still exists a need for a completely stable, highly efficient and thoroughly safe sun protection composition which not only provides a wide spectrum of protection in the ultra-violet region, against the aforementioned short and long term damage to the skin that can result from excessive exposure to sunlight, but which can also ameliorate or prevent skin damage following exposure to other adverse climatic conditions or contact with, particularly immersion in detergent solution liable to cause damage. It is with the fulfillment of these needs that the invention is concerned.